Vauxhall is stepping up development of its luxurious new convertible ahead of its launch at the Paris motor show in September. Despite replacing the Astra TwinTop in the Vauxhall line-up, the new model will not be called Astra and neither will the Calibra name be used.

Instead, the open-top four-seater is tipped to get a new name, just as Vauxhall has opted for the fresh Adam badging for its new city car.

Earlier this year, Vauxhall confirmed that the four-door Astra saloon “completes the current Astra range”, even though the new convertible is just three months from being unveiled.

Although it won’t carry the Astra badge, the new convertible has a structure that takes elements from the Astra and Insignia platforms.

As a result, it is longer than the Astra and has a roomier rear cabin than the last Astra TwinTop, which went out of production in early 2011.

Whereas the old Astra TwinTop had a folding metal roof, the new convertible gets a folding soft-top, which is lighter and packs away more efficiently than a metal design, leaving a much more practical luggage space. These spy pictures reveal the final look of the roof for the first time.

Inside, the new convertible is said to have an upmarket cabin that incorporates high-quality plastics and switchgear, some of which will be used in the facelifted Insignia.

The new convertible is also likely to feature new, downsized 1.6-litre turbo ‘Family 3’ petrol engines, which are due in production later this year.

The most powerful 1.6 GDi will make 197bhp and the less stressed version about 150bhp. The new Family 3 engines feature direct injection and stop-start and the highest-output 197bhp version generates 221lb ft at 1700rpm.

It is said to produce 13 per cent less CO2 than Vauxhall’s existing 1.6T unit, suggesting a sub-150g/km figure in the new convertible.

A brace of diesel engines – likely to be the best-sellers – will also power the soft-top. A 128bhp 1.7 CDTi is understood to be the entry-level oil-burner, and a 165bhp 2.0 CDTi will feature at the top of the range.

Vauxhall is known to be developing a new dual-clutch automatic transmission, although it’s unlikely to be available at the launch of the convertible. Instead, it is expected to arrive about 18 months after launch.

Initially, the convertible will feature a standard six-speed manual gearbox, with a six-speed auto on the options list.

Because the new convertible is bigger and better appointed inside than the old Astra TwinTop, it is likely to be priced slightly higher when UK sales kick off in spring 2013.

Vauxhall will also hope that it will at least match the 3800 average annual sales of the TwinTop, which peaked at 6600 units in 2007.

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Shame GM treated Saab like dirt, perhaps they could have made something like this but with a Saab badge and some decent Scandinavian styling... at least Saabs used to have character, rather than the bland boxes that are known as Vauxhalls and Opels.

Its probably wise that manufacturers are resorting back to the soft top than the folding hard top. i've heard a few horror stories with the big 3 having leaking problems namely Focus CC,Eos and Astra Twintop which presumably problems will only get worse as the car ages. looking forward to this car lets see what they can do with it.

Those of us who know a little about automotive history have realised that GM have called their new city car "Adam" after Adam Opal, the founder of Adam Opal AG. This makes perfect sense in markets where the car in sold under the Opal brand rather than the Vauxhall brand.

Perhaps the car should be renamed the "Vauxhall Alex" for the UK market after Alexander Wilson who founded Alex Wilson and Company, which became Vauxhall Motors.

Put a hard top on it, put it on a Monaro RWD platform, give it a good range of engines (from diesels to twin turbo V6s) and call it Manta.

So, basically, you're asking them to make a completely different car...

I guess they could make a coupe version of the Caddy ATS and badge it as an Opel, but it wouldn't be in this price range, and seeing as Opel/Vauxhall new strategy is moving away from premium status, that seems unlikely.

Apart from the fabric roof this seems to be following what VW did with the Eos, creating a model that fits between two ranges. Hopefully it will be more successful than the Eos, which, in my opinion, has been eclipsed by the far more attractive Golf Cabriolet.